1. Field of the Invention
The present invention relates to image display device and method for stereoscopically displaying a stereoscopic image generated from two or more images to allow stereoscopic viewing of the image, as well as a program for causing a computer to carry out the image display method.
2. Description of the Related Art
It has been known to provide stereoscopic viewing with using parallax by combining two or more images, which are obtained through photographing the same subject from different positions, to generate a stereoscopic image, and stereoscopically displaying the thus generated stereoscopic image. As a specific example of a technique to achieve the stereoscopic display, parallel viewing with naked eyes is known, where the stereoscopic display is achieved by arranging the two or more images side by side. Further, the stereoscopic display may be achieved by generating a stereoscopic image by combining the two or more images, for example, by overlapping the images with changing the colors of the images into colors different from each other, such as red and blue, or by overlapping the images with providing different polarization directions of the images. In these cases, the stereoscopic viewing is effected by using image separating glasses, such as red-and-blue glasses or polarization glasses, to provide a merged view, which is attained via the automatic focusing function of the eyes, of the stereoscopically displayed stereoscopic image (anaglyph system, polarization filter system).
The stereoscopic viewing can also be achieved without using the polarization glasses, etc, by displaying the two or more images on a stereoscopic display monitor which allows the stereoscopic viewing of the images, such as in a parallax barrier system or a lenticular system. In this case, the stereoscopic display is achieved by cutting the two or more images into vertical strips and alternately arranging the strips to generate a stereoscopic image, and disposing a light shielding barrier having slits. Further, a method for providing the stereoscopic display using afterimage effect has been proposed, in which left and right images are alternately displayed by being switched at a high speed with changing the direction of rays from the left and right images through the use of the image separation glasses or attaching an optical element on a liquid crystal display (backlight control system).
When the stereoscopic viewing is provided as described above, a preferred level of stereoscopic effect varies among users who view the stereoscopic images. Since the stereoscopic effect changes depending on an amount of disparity (parallax) between the two or more images for stereoscopic viewing, a technique to generate a stereoscopic image has been proposed, which involves receiving an instruction to control the parallax level of the stereoscopic image while the image is stereoscopically displayed, and generating a modified stereoscopic image according to the instructed parallax level (see Japanese Unexamined Patent Publication No. 2004-129186, which is hereinafter referred to as Patent Document 1). Another technique to generate a stereoscopic image has been proposed, where the stereoscopic effect is controlled while the stereoscopic image being displayed is stereoscopically viewed (see Japanese Unexamined Patent Publication No. 10 (1998)-090814, which is hereinafter referred to as Patent Document 2). A technique to control the stereoscopic effect during a video game has also been proposed (see Japanese Unexamined Patent Publication No. 9 (1997)-192349, which is hereinafter referred to as Patent Document 3).
In the techniques disclosed in Patent Documents 1 to 3, however, although the stereoscopic effect can be changed by adjusting the parallax level, adjustment of the stereoscopic effect is performed with the user viewing the stereoscopically displayed image, and therefore the amount of change of the parallax level is not readily recognized.